Calender rolls



Jan. .30, 1968 s s 3,365,774

- CALENDER ROLLS Filed Oct; 28, 1965 I I 3 Sheets-Sheet 1 INVENTOR.

00 420 KU STEES BY Z Z C A IEYS E. KUSTERS CALENDER ROLLS Jam. 30, 1968 s sheets-sheet s Filed Oct. 28, 1965 INVENTOR AUJTE/PS fowl/Q0 5 1477 EA/EVS 5 Claims. ci. 29-116) This is a continuation-impart of application Ser. No. 354,306, filed Mar. 24, 1964, and now abandoned, which was a continuation-in-part of application Ser. No. 165,- 427, filed Ian. 10, 1962, and now abandoned.

This invention relates to textile and paper calender rolls of the type using a soft roll and at least one hard roll forming a nip through which the textile or paper web passes to receive the calendering action. Often cne soft roll is used with two hard rolls with the single soft roll forming two nips through which the web passesin succession.

In the prior art a soft roll is made of stacked paper or cloth disks tightly compressed together with their edges finished to form a true cylinder. The hard and soft rolls are pressed towards each other under relatively high pressure and these rolls are usually intergeared and driven to obtain slippage between the hard roll and the web to promote the calendering action.

Such soft rolls are easily marked by the edges of the web and by splices or other discontinuities in the webs surface. When this occurs the surface of the roll must be refinished. This requires removing the roll from the calender, machining, and returning the roll to the calender.

This disadvantage, among other disadvantages, has shown the need for improvement.

Press rolls of the type used on paper machines to dewater the wet paper web have been covered tightly with a layer of elastically deformable rubber. The characteristics of rubber make it unsuitable for use as the soft roll of a calender. The physical and chemical characteristics of the synthetic polyamide or superpolyamide materials suggest that such a material, having the proper degree of elasticity, when used instead of rubber should provide a calender soft roll of improved non-marking characteristics while providing a satisfactory calendering action on the Web. For example, the superpolyamide material known .in the USA. as nylon, when used as a covering or sleeve shrunk on a rigid steel roll appears to be suitable for use as a calender soft roll.

With the above in mind, calender soft rolls were made by shrinking a sleeve of superpolyamide material, such as nylon, on a steel roll, but when such soft rolls were placed in service, in particular when operating between two steel counter rolls, they rapidly destroyed themselves. The plastic coverings became lumpy and loosened from the steel rolls.

Thus, the industry was presented with the problem that even though the synthetic polyamide and superpolyamide materials appeared to be very suitable for use as calender soft rolls, such materials cannot be used in the normalmanner in a calender operating-under commercial conditions.

One object-of the present invention is to provide a calender soft roll using effectively an appropriate synthetic United States Patent 0 "ice Y polyamide or superpolyamide material, such as nylon,

and which will be capable of operating with an adequately long service life when used commercially, working opposite a steel counter roll, to calender textile and paper webs. Although intended as a calender roll, such a roll might of course be used for other applications requiring the operation of a soft roll forming a nip with a hard counter roll. I

The present invention is based on several years of thorough testing of plastic covered rolls of various types, the term plastic being used to mean appropriate types of synthetic polyamide and superpolyamide materials.

This testing showed that even a plastic of excellent physical quality has two troublesome properties, namely, poor heat conduction and a very high thermal expansion coeiiicient. It was found that these disadvantages cannot be eliminated but must be compensated for by the 1;011 construction.

To begin with, it was found fundamentally wrong to shrink a plastic cover on a steel shaft or roll. Secondly, it is also wrong to arrange such a plastic covered roll between two or more hard rolls to form two calendering nips. Both must be avoided for the following reasons:

Textile and paper webs are uneven throughout their length and cause an excessive build-up of pressure in a localized area of the plastic tightly covering the roll, which in turn causes local overheating. When this occurs, even for a slight amount, a thick balloon-like bulb is formed by the plastic which cannot move in an axial direction and equalize. The result is excessvie reversals of bending in this localized area causing in turn higher pressure between it and the opposing hard counter roll and further enlargement of the plastic bulbs. This effect continues increasingly and results in localized melting of the plastic covering shrunk on the steel roll.

When the plastic covered soft roll is used with two hard counter rolls to form two nips, the above trouble is accented. In addition, the hard roll of necessity indents the soft roll to form an arcuate indentation. The elasticity of the plastic makes it give as it enters the indented area and recover as it leaves this area. However, all of the polyamide and superpolyamide plastics have the characteristic that there is some delay in their elastic recovery. With commercial calender operating speeds the result is that after leaving one nip area the plastic is not sufiiciently recovered elastically before it enters the next nip, the cumulative action being one of working the plastic plastically rather than completely elastically. The result again is excessive heating.

In all instances the poor heat conductivity of the plastic prevents the heat from being absorbed and carried away by the steel roll on which the plastic sleeve or covering is shrunk. Because of the high thermal coetficient of expansion of the plastic, it expands from its shrunken condition so that with continued operation it becomes loose from its steel roll. Being then in, a heated condition, and because of the other troubles described above, the roll destroys itself.

According to the present invention the ditiiculties described herein above are eliminated by initially castinga hollow cylinder or sleeve from a suitable polyamide or superpolyamide material, such as nylon in the U.S.A.,- and using the necessary support steel or other roll somewhat loosely on the inside of this shell with the latters ends free from tight restraint. In other words, what may be called the plastic covering is made initially at least slightly loose in all directions with respect to the roll it encompasses before being placed in service in a calcn-.

der. Only one hard counter roll is used, to avoid distorting the sleeve into an elliptical shape. The sleeve is cast Ythe supporting roll within the sleeve should be designed to maintain a uniform pressure throughout the length of I the nip formed by the shell and counter roll, in a lengthwise or axial direction.

With the above arrangement any tendency of the plastic sleeve to form a balloon-like bulb is overcome because the bulb can move in an axial direction under the nip pressure and prevent the excessive localized action resulting from a tightly shrunk plastic cover on a steel roll. Any means used to maintain the radial alignment between the loose sleeve and its steel support roll should permit slight endwise or axial movement of the sleeve relative to its support roll. Because the sleeve is running freely between the hard counter roll and the sleeves support roll the sleeve can expand and contract in all directions without introducing problems other than the need for an adjustment of the nip pressure to keep it constant, and this can be done automatically by known means.

Rolls constructed as described generally above when put in calendering service under commercial operating conditions have not only the non-marking advantage expected of the plastic as an improvement over prior art soft rolls, but important additional advantages. For example, it was found that the elastic deformation and recovery of the plastic in the nip formed by the plastic sleeve with the hard roll, exerts a slipping action relative to the hard roll providing greatly improved calendering effects and in some respects previously unobtainable effects. Because of this slipping action it is unnecessary to intcrgear the hard and soft rolls as was usually necessary when using the prior art soft rolls.

Examples of the present invention are illustrated by the accompanying drawings in which:

FIG. 1 schematically shows in cross-section one example;

FIG. 2 schematically shows in cross-section a second example wherein two rolls of the present invention co owl-ate with a single hard roll to form two calenden'ng nips;

FIG. 3 is a vertical section of a commercial form of calender using the present invention, taken on the line 33 in FIG. 4; and

FIG. 4 is a vertical section taken on the line 4-4 in FIG..3.

Referring first to FIG. 1, the synthetic polyamide or superpolyamide material, having the appropriate physical properties for use as a calendar soft roll, is cast to form the cylindrical sleeve 1. Such a sleeve may be formed by the centrifugal casting process. The plastic is block polymerized, sometimes also called mass, bulk or cast polymerization. That is to say, no solvent or dispersing medium is used. The sleeve should have a cylindrical contour both inside and outside and be of uniform wall thickness. The outside diameter of course depends on the requirements of the calender for which the roll is intended. The support roll 2 is shown on the inside of the sleeve 1, and its outside diameter is related to the inside sleeve diameter to leave a slight space 3 between the two which is at a maximum diametrically opposite to the hard roll 4 which forms the calendering nip with the sleeve 1. This maximum space, or the play between the two, need be only from 1 to 3 mm.

The rolls 2 and 4 are provided with means (not shown) for pressing them together to develop the necessary calendering roll pressure. The wall thickness of the sleeve 1 is related to this roll pressure so that the elastic dC-' formation of the sleeve 1 at the nip, caused by the pressure between the rolls 2 and 4, does not extend completel y through the sleeve 1 in a radial direction. Thus, if the elastic deformation of the sleeve 1 produced by the roll 4, indicated by the broken line 5, and the de formation produced by the pressure of the roll 2., indicated by the broken line 6,. should actually meet or overlap, instead of being radially spaced as shown in FIG. 1, an undesirable distortion effect may result.

When the hard counter roll 4 has the smaller diameter,

as would be usual, it forms an appreciable indentation in the sleeve 1, as indicated at 7 in FIG. 1. A somewhat lesser deformation (not shown) results from the pressure of the support roll 2 because of its larger diameter. When the roll 2 is driven to drive the shell 1 rotatively the roll 4 is frictionally driven by the Web w which passes through the nip which may be said to be represented by the indentation 7. Customarily, the hard roll 4 is heated as by the heating means 8 indicated in the schematic FIG. 1, and to prevent overheating of the shell 1 the roll 2 may be provided with cooling means indicated at 9. The hard roll may be driven instead of the soft roll.

Ordinarily, the support roll 2 is made longer than the sleeve 1 so that it may be joumaled in the calender frame members and means are provided, as described hereinafter, to prevent excessive axial displacement of sleeve 1 relative to the roll 2.

In operation, as with the support roll 2 rotatively driven to frictionally drive the loosely mounted plastic sleeve 1 the web w is driven linearly to rotate the counter roll 4, no intergearing between the two rolls being needed. The elastic properties of the plastic permit the indentation 7 formed by the counter roll 4 pressing the web w into the plastic sleeve 1, to be extensive enough to obtain throughout the zone it forms substantial radius differences relative to the axis of rotation, thereby first slowing the web in its linear travel and then accelerating this travel relative to the counter roll 4 to obtain the very effective calendering action previously described.

The roll lengths involved should notbe' sufficient to permit the roll pressure to cause roll flexure or deflection sufficient to materially alter the nip pressure in a lengthwise direction or axially with respect to the rolls.

As the sleeve 6 becomes heated it is entirely free to expand and contract in all directions due to its loose association with respect to the roll 2 on which it is mounted. This provides the advantages previously described.

When two roll nips are desired the conventional use of two hard rolls and one soft roll cannot be used. As shown by FIG. 2, only the one hard roll 4 should be used and the soft roll illustrated by FIG. 1 should be used in duplicate, one on either side of the roll 4 as required to form two nips through which the web w may pass in succession.

Under practical working conditions, the plastic used may be a centrifugally cast block polymerized sleeve of synthetic superpolyamide plastic, such as nylon, having a modulus of elasticity of over 15,000 kg./cm. when measured after the casting has been conditioned by receiving an aging period of at least 14 days. The rolls 2 and 4 may of course be made of steel and should be short and absolutely rigid unless the roll 2 is of the controlled deflection type such as shown, for example, by the Appenzeller Patent 2,908,964, issued Oct. 20, 1959. Calendering pressures exerted on the web w in the nip area indicated at 7 in FIG. 1, may be up to the order of 350-700 kg./cm., and the wall thickness of the shell 1 should be sufficiently thick to prevent the deformations of the shell, at the nip, caused by the two opposing pressure applying rolls 2 and 4, from intersecting radially. Preferably there should be a substantial thickness of plastic between these zones.

One commercialized form of calender using the present invention is illustrated by FIGS. 3 and 4. In this case, the hard roll 4a is stationarily journaled by bearings 10 in the side frame members 11 of the calender. Two rolls made according to the present invention are located above shown at 1a and the support rolls for these sleeves being shown at 2a. The support rolls 2a are made as described by the previously described Appenzeller patent or, in other words, are of the control deflection type having an inner core or beam 12 provided with projections or extensions 13 mounted by rocking bearings 14 in the front ends of two-armed levers 15 rockingly mounted by the frame members 11 and having their back ends adapted to be thrust apart by hydraulic thrusters 16. The thrusters 16 serve to push or press the upper and lower soft rolls against the counter roll 4a to provide equal nip or calendering pressures on the top and bottom of the roll 4a.

In this case it is the roll 4a which is driven, one roll neck 4b which is journaled by the bearings 10 projecting outwardly as at 4c so it can be connected to rotary power;

In accordance with the previously mentioned Appenzeller patent the beams or cores 12 are provided with oil seals generally indicated at 17 which divide the space formed between the beam 12 and the seals 17 into upper and lower chambers. Oil under pressure is introduced through inlet passages 18 to the chambers formed between the seals 17 and the shell forming in effect the roll 2a. In other words the roll 2a is a hollow shell or roll, and this shell is journaled relative to the beam 12 by bearings 19, the beam 12 being non-rotative. Oil pumped through the passage 18 under pressure exerts a pressure between the beam 12 and the shell 2a as to each roll and since this is hydraulic pressure it is absolutely uniform throughout the length of the shell 2a, the beam 12 deflecting under the hydraulic load. Leakage through the seals 17 is removed from the other or low pressure chamber by way of a passage 20. Other types of controlled deflection rolls may be used.

The plastic shells 1a are in each instance. held against excessive axial displacement relative to the rolls 2a, by end collars 21 locked to the hollow rolls 2a adjacent their ends. The counter roll 4 may have a passage 22 for receiving heating fluid and the hydraulic leakage passed by the seals 17 provides the illustrated controlled deflection rolls with a cooling means because of the oil circulation thus established.

In operation the web is passed through the two nips formed by the two soft rolls and the hard counter roll, in the general fashion shown by FIG. Zexcepting that in this case there is a difference caused by the rolls being in ver tical alignment. The shells 1a are made rather substantially thicker than is required to prevent the deformation produced by the rolls 2a and 4a from meeting or overlapping radially. The shells 1a are completely free to expand and contract as previously described, although as they expand adjustments should be made, preferably by automatic means, as :required to keep the roll pressure uniform. All of the previously described advantages are obtained. In addition, the use of the controlled deflection rolls permits the roll length to be as great as is normally required for calendering even the wider widths of textile and paper web. The roll nip pressure is maintained uniformally from end to end or lengthwise with respect to the rolls.

No gear-ing is shown between the rolls 2a and the counter roll 4a and none is required. This is an advantage because such gearing is necessarily located inside one or both of the frame members of the calender, where the .gearing is exposed so it can cause trouble. In addition, ex-

6 of the plastics having a modulus of elasticity of more than about 15,000 kg./cm. In other words, a highly elastic plastic should be used.

The'rotative support roll inside of the sleeve presses the latter against the textile or paper web when the latter is passed through the nip formed between the sleeve and a hard counter roll. The support roll may be made. of solid metal when the roll length is not excessive, and when longer roll lengths are involved so as to introduce the risk of roll deflection or flexure, an etficient controlled deflection roll should be used. In other words, the roll pressure existing throughout the nip formed by the hard and soft rolls should be uniform throughout the length of I the roll nip.

The sleeve should be loose from the support roll both radially and axially at least to a degree permitting'the sleeve to thermally expand and contract freely relative to the support roll. The sleeve should have a wall thickness sufficient to prevent its deformation under the pressures caused by its support roll and the web pressed against the sleeve by the hard counter roll, from radially intersecting under such pressures. Suitable plastics should be able to operate under such conditions when roll pressures up to from 350-700 kg./cm. are involved. In prac-. tical work the necessary wall thickness of the sleeve can be determined by the fact that if made too thin the sleeve will be subjected to plastic working causing its overheating and ultimate destruction. The maximum wall thickness is determined by the size of its support roll which is, in turn, dictated by the combination of roll pressuresand roll lengths involved. With these principles understood the proportioning of the sleevebecomes a matter of engineering. 7

It has been the use of such general principles that has made commercially possible the use of the described kind of plastic as the soft roll surface of textile and paper calenders wherein the plastic surface forms a nip with a sists of a hollow circular cylinder of said plastic, and in' that a rotating relatively hard backing roll is located in said hollow cylinder, the outside diameter of said backing roll being slightly less than the inside diameter of said plastic hollow cylinder, said backing roll resting on the internal circumference of said hollow cylinder only along an internal longitudinal line lying opposite to the circumferential longitudinal line of said hollow cylinder which contacts the web material, said hollow cylinder being made of a polyamide or superpolyamide plastic having a modulus of elasticity of more than 15,000'kg. per sq. cm.

2. A roll press as in claim 1, characterized in that the polyamide or superpolyamide plastic hollow roll is a centrifugally cast block polymerized cylinder and said minimum modulus of elasticity is provided by this cylinder in a conditioned state after aging for at least 14 days.

3. A roll press as claimed in claim 1, characterized 4,

in that the wall of the polyamide or superpolyamide plastic hollow cylinder is of such thickness that when the roll press is in normal operation the deformations of the plastic arising externally from the contact of the cylinder with the web material, and the deformations of the plastic arising from the contact of the internal backing roll on 4. A roll press as in claim 1, characterized in that said hard backing roll is a controlled deflection roll.

5. A roll press as in claim 1, characterized in that the polyamide or superpolyamide plastic hollow roll is a centrifugally cast block polymerized cylinder and said minimum modulus of elasticity is provided by this cylinder in a conditioned state after aging for at least 14 days and being further characterized in that the wall of the polyamide or superpolyamide plastic hollow cylinder is of such thickness that when the roll press is in normal opera tion the deformations of the plastic arising externally from the contact of the cylinder with the web material, and the deformations of the plastic arising from the contact of the internal backing roll on the internal circumference of said hollow cylinder, do not overlap under working pressures up to about from 350-700 kg./cm.

References Cited UNITED STATES PATENTS 3,222,209 12/1965 Brundige et al 29-132 X 8 959,067 5/1910 Palmer. 1,739,572 12/1929 Bidwell ro -92 1,868,860 7/1932 VonI-Reis 100-162 2,312,762 3/1943 Kauffman 68-253 2,344,274 9/1944 Stacom 100--160' 2,908,964 10/1959 Appenzeller 29-110 2,950,507 8/1960 Keyser.

OTHER REFERENCES Modern Plastics Magazine Encyclopedia Issue for 1961, September 1960, vol. 38. I

Plastics Properties Chart, Part 1, Thermoplastics, found in inside rear cover of Modern Plastics Encyclopedia Issue 15 for 1959, September 1958, vol. 36.

LOUIS O. MAASSEL, Primary Examiner. 

1. A ROLL PRESS FOR THE PRESSURE TREATMENT OF WEB MATERIAL IN WHICH A PLURALITY OF ROLL CO-OPERATE, AT LEAST ONE OF SAID CO-OPERATING ROLLS HAVING A WEB MATERIAL CONTACTING CIRCUMFERENCE OF POLYAMIDE PLASTIC OR SUPERPOLYAMIDE PLASTIC, CHARACTERIZED IN THAT THE ROLL HAVING THE POLYAMIDE OR SUPERPOLYAMIDE PLASTIC CIRCUMFERENCE CONSISTS OF A HOLLOW CIRCULAR CYLINDER OF SAID PLASTIC, AND IN THAT A ROTATING RELATIVELY HARD BACKING ROLL IS LOCATED IN SAID HOLLOW CYLINDER, THE OUTSIDE DIAMETER OF SAID BACKING ROLL BEING SLIGHTLY LESS THAN THE INSIDE DIAMETER OF SAID PLASTIC HOLLOW CYLINDER, SAID BACKING ROLL RESTING ON THE INTERNAL CIRCUMFERENCE OF SAID HOLLOW CYLINDER ONLY ALONG AN INTERNAL LONGITUDINAL LINE LYING OPPOSITE TO THE CIRCUMFERENTIAL LONGITUDINAL LINE OF SAID HOLLOW CYLINDER WHICH CONTACTS THE WEB MATERIAL, SAID HOLLOW CYLINDER BEING MADE OF A POLYAMIDE OR SUPERPOLYAMIDE PLASTIC HAVING A MODULUS OF ELASTICITY OF MORE THAN 15,000 KG. PER SQ. CM. 